This invention relates to a function separated type electrophotographic light-sensitive member comprising an electrically conductive support, a light-sensitive layer made up of amorphous silicon and an electric charge transport layer. More particularly, it relates to a function separated type electrophotographic light-sensitive member comprising an electrically conductive support, an amorphous silicon layer, and an electric charge transport layer into which photocarriers produced in the amorphous silicon layer by irradiation with electromagnetic wave can be efficiently injected.
Light-sensitive members comprising amorphous selenium (Se) or amorphous Se doped with impurities such as As, Te, Sb, Bi, etc., or comprising of CdS, etc., have heretofore been used as electrophotographic light-sensitive members. However, these light-sensitive members suffer from many problems; for example, they are toxic, their heat stability is very poor because the photoconductive substances crystallize at 100.degree. C. or more, and their mechanical strength is low.
Recently, therefore, a method has been developed in which amorphous silicon is used to provide an electrophotographic light-sensitive member having no toxicity, high heat stability, high mechanical strength, and high photoconductivity. However, those light-sensitive members made up of amorphous silicon (containing no dopants) are not desirable as electrophotographic light-sensitive members because their specific resistance in a dark place is as low as 10.sup.5 .OMEGA..multidot.cm, and the photoconductivity thereof is small.
This is due to the fact that in the atomic arrangement of amorphous silicon, many Si-Si bonds are cut or broken, and there are many latice defects: that is, the hopping conduction of carriers owing to a high density of localized state in energy gap of 10.sup.20 cm.sup.-3 lowers the specific resistance in darkness, and the trapping in the defects of photo-excited carriers deteriorates the photo-conductivity. On the other hand, in amorphous silicon obtained by doping with hydrogen, the density of localized state in energy gap is reduced to 10.sup.17 cm.sup.-3 or less by the compensation of the defect through the formation of Si-H bonds therein, resulting in an increase of the specific resistance in a darkness to 10.sup.8 .OMEGA..multidot.cm or more, and thus the photoconductivity is improved, and physical properties desirable for an electrophotographic light-sensitive member are obtained.
However, the specific resistance in darkness of the amorphous silicon is from 1/100 to 1/1000 of that of the amorphous Se. This gives rise to the problems that the dark decay rate of the surface potential in darkness is high and the initially charged potential is low. In order to obtain a sufficient initially charged potential, therefore, it is necessary to increase the thickness of the light-sensitive layer to about 50.mu. or more. In general, the amorphous silicon film is produced by glow discharge or sputtering, and it takes an unduly long period of time to produce an amorphous silicon film having a thickness of 50.mu. or more according to such a technique, which is undesirable from an industrial viewpoint. Furthermore, such a thick amorphous silicon film is poor in flexibility and therefore, when it is provided on a support having high flexibility, cracking of the silicon film easily occurs.